Electromagnet and actuating mechanism for switch device, using thereof

ABSTRACT

An electromagnet includes a coil, a movable iron core adapted to move on the center axis of the coil, and a stationary iron core provided so as to cover the upper and lower surfaces and the outer peripheral surface of the coil. A permanent magnet is arranged in a gap surrounded by the movable iron core and the stationary core.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an electromagnet and as well toan actuating mechanism using thereof for a switching device, and inparticular to an electromagnet for restraining demagnetization of apermanent magnet, and as well to a reliable operating mechanism usingthereof for a switching device.

RELATED ART

[0002] As to the actuating mechanism for a switching device, there havebeen provided an electric power driven spring actuating mechanism, and ahydraulic or pneumatic actuating mechanism. These mechanism have a largenumber of components so as to have a link mechanism which iscomplicated, resulting in a relatively high manufacturing cost. Anoperating mechanism using an electromagnet is used as one of measuresfor simplifying the link mechanism. For example, JP-A-5-234475 disclosesa vacuum contactor in which an electromagnet is used for turn-onoperation so that a closing spring which has been stored with energy isreleased simultaneously with the turn-on operation in order to opencontacts. Further, in an actuating mechanism disclosed inJP-A-10-249092, a plunger is provided extending through two turn-on and-off coils so that both turn-on and turn-off are carried byelectromagnet. Further, JP-A-2000-249092 discloses an actuatingmechanism which maintains a turn-on condition with the use of anattraction force of a permanent magnet, and turn-off operation iscarried out with the use of springs for driving movable members, whichare provided respectively, by reversely energizing a coil with coilcurrent. In this case, it is advantageous since only a single coil isrequired for both turn-on and turn-off.

[0003] However, the conventional electromagnet incorporating a permanentmagnet has raised following disadvantages: a permanent magnet may be arare-earth samarium cobalt group magnet, a neodymium group magnet, analnico group magnet, a ferrite group magnet or the like. If theneodymium group magnet which has a high residual magnetic flux densityand which has a relatively low cost is used, an electromagnet can besmall-sized and manufactured at a relatively low cost. However, theneodymium group magnet has a high magnetic coercive force, that is,1,000 KA/m so as to require a magnetized electric field which is higherthan 2,000 KA/m (corresponding to a magnetic flux density of 2.5 T).Accordingly, it is unpractical to magnetize a permanent magnet with acoil of an incorporated electromagnet, and accordingly, a magnet has tobe incorporated after being magnetized.

[0004] In the case of application of an electromagnet for a actuatingmechanism for a switching device, reliable operation for a long termgreater than 20 years and by a huge number of operating times arerequired. Accordingly, factors which cause demagnetization of apermanent magnet should be eliminated as possible as it can. Anelectromagnet incorporating a permanent magnet as disclosed in theJP-A-2000-249092, a backing magnetic field is applied to the permanentmagnet, direct thereto so as to carry out cut-off operation. Therepetition of application of reverse energy to the permanent magnetcauses a risk of demagnetization of the permanent magnet or lowering ofthe use life thereof.

[0005] Further, if a permanent magnet is present on a magnetic path, amagnetic resistance as viewed from a coil becomes higher. Since thepermeability of a permanent magnet is substantially equal to that of theair, a gap which is equal to a sum of a stroke length and the thicknessof the permanent magnet is present at, the time of a start of operation,and accordingly, a greater ampere turn is required.

[0006] Further, metrication errors caused during manufacture areinevitable for the thickness of the permanent magnet and the core, andthe gap between the permanent magnet and the movable core which isopposed to the former and which can extend and retract, at an end of thestroke of the latter varies. Further, this gap causes the turn-oncharacteristic, the cut-off characteristic and the turn-on conditionholding force (attraction force) to vary. However, should the allowablerange for metrication errors, that is, the tolerance be strictlymanaged, the manufacture of an inexpensive electromagnet could be hardlybe produced.

SUMMARY OF THE INVENTION

[0007] The present invention is devised in order to solve theabove-mentioned problems, and an object of the present invention is toprovide an electromagnet having a long use life and a high degree ofefficiency, in which no backing magnetic field is applied to a permanentmagnet, and further, no permanent magnet is present in a magnetic pathwhich is created by a coil current, and as well to provided an actuatingmechanism for a switching device, using the electromagnet.

[0008] Another object of the present invention is to provide anelectromagnet in which the gap between the permanent magnet and themovable core which is opposed to the former and which can extend andretract can be simply adjusted.

[0009] According to the present invention, there is provided anelectromagnet comprising a coil, a movable iron core which is moved onthe center axis of the coil, a stationary iron core which is provided soas to cover upper, lower and outer peripheral surfaces of the coil, anda permanent magnet located in a gap defined by the movable iron core andthe stationary iron core, wherein the movable core is attracted to thestationary core by a magnetic field produced by the permanent magnet.

[0010] Further, according to the present invention, there is provided anelectromagnet comprising a coil, a movable iron core which is moved onthe center axis of the coil, a stationary iron core which is provided soas to cover upper, lower and outer peripheral surfaces of the coil, thestationary core is provided, on such a side that the movable iron coreis inserted, with a magnetic protrusion, and the movable iron core beingcomposed of a plunger and a steel plate secured to one end part of theplunger so that an end face of the plunger and the stationary iron core,and the steel plate and the protrusion are opposed to each other in thesame directions, respectively, and a permanent magnet provided in a zonewhich is defined by the plunger, the protrusion, the steel plate and thestationary iron core.

[0011] Further, according to the present invention, there is provided anelectromagnet comprising a coil, a movable iron core which is moved onthe center axis of the coil, a stationary iron core which is provided soas to cover upper, lower and outer peripheral surfaces of the coil, thestationary core is provided, on such a side that the movable iron coreis inserted, with a magnetic protrusion, the movable iron core beingcomposed of a plunger and a steel plate secured to one end part of theplunger, and a permanent magnet provided in a gap defined by theplunger, the protrusion, the steel plate and the stationary iron core, aside surface of the steel plate and the protrusion being opposed to eachother, and an end face of the plunger and the stationary iron core, andthe steel plate and the permanent magnet being opposed to in the samedirection, respectively.

[0012] Further, according to the present invention, there is providedthe electromagnet as mentioned above, which incorporates a power sourcecircuit for selectively applying a forward or reverse current to thecoil, and accordingly, when the forward current is applied, a magneticfield is produced in a direction the same as a direction of a magneticfield produced by the permanent magnet so as to effect attraction, andwhen the reverse current is applied, the magnetic field produced by thepermanent magnet is cancelled so as to effect release action.

[0013] Further, according to the present invention, there is provided anelectromagnet including a coil, a movable iron core which is moved onthe center axis of the coil, a stationary core configured to cover bothaxially end surfaces and the outer peripheral surface of the coil, and apower source for applying a forward current and a reverse current to thecoil, wherein the movable iron core is moved toward the stationary corewhen the forward current is applied to the coil, characterized in thatthe stationary iron core includes an iron core upper member configuredto cover one of the axial end surfaces of the coil, a permanent magnetis located on the upper surface of the stationary iron core upper memberwhile the movable iron core includes a planer plate member having asurface opposed to the upper surface of the stationary iron core withthe permanent magnet intervening therebetween, and a plunger memberhaving a cylindrical surface opposed to the inner peripheral surface ofthe coil, the inner peripheral surface of the stationary iron core uppermember and the cylindrical surface of the plunger member definestherebetween a gap g1 which is smaller than the axial thickness t of thestationary core of the permanent magnet.

[0014] A magentic member may be interposed between the end surface ofthe plunger member on the planer plate side, and the planar platemember.

[0015] The permanent magnet may be the one selected from a groupconsisting of a rare earth samarium-cobalt group magnet, an alnico groupmagnet a ferrite group magnet.

[0016] Further, according to the present invention, there is provided anactuating mechanism for a switching device, incorporating theabove-mentioned electromagnet, separatable contacts, a cut-off springfor opening the contacts, a power source circuit for selectivelyapplying forward and reverse current to the coil wherein when theforward current is applied, the cut-off spring is urged while thecontacts are turned on so as to hold the turn-on condition by attractionforce of the permanent magnet, and when the reverse current is appliedto the coil, a magnetic field produced by the permanent magnet iscancelled out so that the opening and closing device is cut off by aforce of the cut-of spring.

[0017] That is, with the electromagnet, constituted as mentioned above,in which a magnet field causing a reverse current to run through thecoil does never extend through the permanent magnet upon cut-off, thepermanent magnet can be prevented from being reversely excited andfurther, no permanent magnet is present in a magnetic path created bycoil current so that no factor of demagnetizing the permanent magnet ispresent, resulting in the possible use of a neodymium group magnet,thereby it is possible to provide an electromagnet having a long uselife and a high degree of efficiency.

[0018] Further, by changing the thickness of a magnetic memberinterposed between the end surface of the plunger member on the planerplate member side, and the planer plate or changing the number of thinplanar plate members which constitute the magnetic member, the gapbetween the permanent magnet and the movable iron core which is opposedto the former and which can extend and retract, at a stroke end, can beadjusted. That is, the characteristics thereof can be stabilized withoutcausing the tolerance of components of the permanent magnet to bestrict, thereby it is possible to provide an inexpensive electromagnetwith a high degree of accuracy.

[0019] Further, with the application of the electromagnet in theactuating mechanism for a switching device, the switching device can besmall-sized and inexpensive and can offer a high degree of reliability.

[0020] The present invention will be detailed in the form of preferredembodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0021]FIG. 1 is a sectional view illustrating an electromagnet in anembodiment of the present invention;

[0022]FIG. 2 is a view illustrating the electromagnet in the embodimentof the present invention in a condition just after a start of attractionthereof;

[0023]FIG. 3 is a view illustrating the electromagnet in the embodimentof the present invention in a condition just before completion ofattraction thereof;

[0024]FIG. 4 is a view illustrating the electromagnet in the embodimentof the present invention in a condition in which attraction of theelectromagnet is completed;

[0025]FIG. 5 is a view illustrating the electromagnet in the embodimentof the present invention in a condition in which, the electromagnet ison release operation;

[0026]FIG. 6 is a view illustrating an electromagnet in a secondembodiment of the present invention in a condition just after a start ofattraction of the electromagnet;

[0027]FIG. 7 is a view illustrating the electromagnet in the secondembodiment of the present invention in a condition just before thecompletion of attraction thereof;

[0028]FIG. 8 is a view illustrating the electromagnet in the secondembodiment of the present invention in a condition in which theelectromagnet is on release operation;

[0029]FIG. 9 is a view illustrating an electromagnet in a thirdembodiment, in a turn-on condition;

[0030]FIG. 10 is a view illustrating the electromagnet in the thirdembodiment, in a turn-off condition;

[0031]FIG. 11 is a view illustrating the electromagnet in the thirdembodiment in the third embodiment during turn-on operation;

[0032]FIG. 12 is a view illustrating the electromagnet in the thirdembodiment in the third embodiment during turn-off operation;

[0033]FIG. 13 is a view illustrating a structure of a vacuum switchingdevice in which the electromagnet according to the present invention isapplied;

[0034]FIG. 14 is a view illustrating a structure of a peripheral part ofa press-contact spring 43 in the vacuum switching device shown in FIG.13; and

[0035]FIG. 15 is a view illustrating an example of a coupling type of aplurality of electromagnets used in the vacuum switching deviceaccording to the present invention; and

[0036]FIG. 16 is a view illustrating another example of the couplingsystem of a plurality of electromagnets incorporated in the vacuumswitching device according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

[0037] Explanation will be made of preferred embodiments of the presentinvention with reference to FIGS. 1 to 13.

[0038] (Embodiment 1)

[0039] Explanation will be made of a first embodiment of the presentinvention with reference to FIGS. 1 to 5.

[0040] Referring to FIG. 1 which is a sectional view illustrating anelectromagnet 10 in the first embodiment of the present invention, theelectromagnet 10 has an axially symmetric structure. In this figure,reference numerals are attached to elements shown on the right half ofthe figure for explaining the structure of the electromagnet 10, and amagnetic field B (indicated by the chain line) which is effected by apermanent magnet 12 and current running through a coil 3 is shown in theleft half of the figure.

[0041] A movable core 1 is composed of a plunger 5 extending through thecoil on the center axis thereof, and a dick-like steel plate 6 securedto one end part of the plunger 5, and is coupled to a load W by means ofa nonmagnetic coupling member 7 secured to an end part of the plunger 5.The load W effects a force which urges the movable iron core 10 upwardunder attraction of the electromagnet 10. A stationary iron core 2 iscomposed of a steel pipe 2 a, a convex steel member 2 b and a ring-likesteel plate 2 c which are all magnetic. The convex steel member 2 b andthe ring-like steel plate 2 c may be attached in such a manner that theyare screwed into opposite ends of the steel pipe 2 a, as shown.Alternatively, they may be secured by welding. Further, the steel pipe 2a and the convex steel member 2 b, or the steel pipe 2 a and thering-like steel plate 2 c may be produced from a columnar material bycutting. Although, the convex steel member 2 b is used in thisembodiment, instead thereof, a mere planar plate may be used. However,in this case, it has been found that if a gap X between the end face ofthe plunger 5 and the stationary iron core 2 is present in the vicinityof the center of the coil 3, leakage fluxes can be reduced, andaccordingly, the convex steel member is more preferable. Further, theconvex steel member 2 b may be formed in one unit body, or may be formedof two steel plates which are joined to each other. The coil 3 iscomposed of a bobbin 3 a made of insulator or nonmagnetic metal(aluminum, copper or the like), and windings 3 b.

[0042] The ring-like steel plate 2 c is screwed into the steel pipe 2 a,being relatively deep therein, and has a configuration formed with amagnetic protrusion 4. In this embodiment, the electromagnet 10 has sucha configuration that the end face of the plunger 5 and the convex steelmember 2 b, and the disc-like steel plate 6 and the protrusion 4 areopposed in the same direction, respectively. The distance g between theside surface of the plunger 15 and the ring-like steel plate 2 c isshorter than the stroke length of the movable iron core. The distance Xbetween the end face of the plunger 5 and the convex steel member 2 b isset to be shorter than a distance L between the disc-like steel plate 6and the protrusion 4, and upon completion of attraction, the plunger 5and the convex steel member 2 b are made into contact with each other.

[0043] A ring-like permanent magnet 12 is located in a zone defined bythe plunger 12, the disc-like steel plate 6, the protrusion 4 and thering-like steel plate 2 c, and is secured on the ring-like steel plate 2c. Reference numeral 13 denotes a retainer which is made of nonmagneticmaterial such as SUS, for the permanent magnet 12, and which is securedby being screwed into the steel pipe 2 b. A gap is defined between thepermanent magnet 12 and the protrusion 4 by the retainer 13 in order toprevent magnetic fluxes produced by the permanent magnet 12 from beingshort-circuited by the protrusion 4.

[0044] Explanation will be made of the electromagnet 10 in thisembodiment of the present invention with reference to FIGS. 2 to 5 inwhich FIG. 2 shows a condition just after a start of attraction, FIG. 3shows a condition just before completion of attraction, FIG. 4 is acondition just after completion of attraction and FIG. 5 is a conditionduring release operation.

[0045] When the coil 3 is energized by an external power source circuit(which is not shown), an attraction force FO is effected at the end faceof the plunger, and accordingly, the movable iron core 1 starts itsdownward motion. At this time, a distance g between the side surface ofthe plunger 5 and the ring-like steel plate 2 c is set to be shorterthan the stroke length of the movable iron core 1, a magnetic field Bcproduced by a coil current passes through a magnetic path 01. It isrequired t that the direction of the coil current and the polarity ofthe permanent magnet 12 have been previously set so that the magneticfield Bc and a magnetic field Bm produced by the permanent magnet 12 areextended in a direction indicated by the arrow shown in FIG. 2. It isnoted that the directions of the magnetic field Bc and the magneticfield Bm may be reversed from each other, simultaneously.

[0046] When the movable iron core 1 is driven by the attraction forceFO, a condition shown in FIG. 3 is effected immediately. Along with thedisplacement of the movable iron core 1, the gap L between the disc-likeiron plate 6 and the protrusion 4 is decreased to a value which issmaller than the gap g between the plunger 5 and the ring-like steelplate 2 c (g>L). Thus, the magnetic field Bc by the coil currentbranches into a magnetic path 02, and it runs through the magnetic path02 by a substantially all amount. That is, along with the movable ironcore 1, in addiction to the attraction force FO effected at the end faceof the plunger 5, an attraction force F1 is effected between thedisc-like steel plate 6 and the protrusion 4. It is noted that in acondition just before completion of the attraction, the magnetic fieldBm of the permanent magnet 12 runs through a magnetic path 03, andaccordingly, the attraction force FO is increased.

[0047] After completion of the operation of the movable iron core 1,when the current running through the coil 3 is cut off, an attractingcondition is held by the attraction force of the permanent magnet 12.Even after completion of the attraction, the magnetic field Bm producedby the permanent magnet 12 passes through the magnetic path 03 since thegap is present between the disc-like steel plate 6 and the protrusion 4.Due to the attraction force FO, the attraction between the movable ironcore 1 and the stationary core 2 is maintained.

[0048] Explanation will be made of release operation with reference toFIG. 5. The release operation is effected by passing a current throughthe coil 3 in a direction reverse to that of the current applied duringthe attracting operation. A magnetic field produced by this coil currentruns through the magnetic path 02 so as to cancel out the magnetic fieldBm produced by the permanent magnet 12. Accordingly, the attractingforce FO exerted to the end face of the plunger 5 is decreased, andtherefore, the movable iron core 1 is moved upward by a load force. Itis noted that since an attracting force Fr is effected between thedisc-like steel plate 6 and the protrusion 4 by the magnetic field Bc atthe same time, should excessive current be applied to the coil 3,attracting operation would possibly be again effected. Thus, it isrequired to provide a means for limiting the coil current through abalance with the load forcer, and for cutting off the coil current atonce after completion of the release operation.

[0049] Next, explanation will be made of technical effects andadvantages of the present invention. As to a conventional electromagnetincorporating a permanent magnet, a permanent magnet 12 is present on amagnetic path created by coil current, and accordingly, the permanentmagnet 12 is directly excited in a reverse direction during releaseoperation. With the repetitions of application of reverse power to thepermanent magnet 12, there would be a risk of demagnetization. In theelectromagnet of this embodiment, the permanent magnet 12 is located ina gap defined by the movable iron core 1 and the stationary iron core 2,that is, in a zone which are magnetically shielded, and according, themagnetic field Bc produced by the coil current can be prevented fromacting directly upon the permanent magnet 12. Even during the releaseoperation, reverse power is never applied to the permanent magnet 12.There by it is possible to provide a magnetic disc 12 which caneliminate the risk of demagnetization, and which can have a long uselife and a high degree of the magnet.

[0050] Further, the magnetic permeability of the permanent magnet 12 issubstantially equal to that of the air, and if the permanent magnet 1 ispresent in the magnetic path created by the coil current, the magneticresistance as viewed from the coil becomes higher. Upon a start of theoperation, a gap which is the sum of the stroke and the thickness of thepermanent magnet 12 is present, and accordingly, the ampere turnrequired for the operation is increased. However, since no permanentmagnet is present on the magnetic path created by the coil current inthe electromagnet 10 according to this embodiment, the magneticresistance is low, and accordingly, the efficiency becomes higher.

[0051] (Embodiment 2)

[0052] Explanation will be made of a second embodiment with reference toFIGS. 6 and 7.

[0053]FIG. 6 is a sectional view illustrating an electromagnet 10 in asecond embodiment of the present invention. A movable iron core 1 iscomposed of a plunger 5 extending through a coil 3 along the center axisof the latter, and a disc-like steel plate 6 secured to one end part ofthe plunger, and is coupled to a load through the intermediary of anonmagnetic coupling member 7 secured to the other end part of theplunger 5. A stationary iron core 2 is composed of a steel pipe 2 a, aconvex steel member 2 b and a ring-like steel plate 2 c which are allmagnetic. The convex steel member 2 b and the ring-like steel plate 2 cmay be attached to the opposite ends of the steel pipe 2 a, beingscrewed thereinto. Alternatively, they may be secured thereto bywelding. The convex steel member 2 b may be manufactured in one unitbody, but it may be formed of two steel plates connected to each other.The coil 3 is composed of a bobbin 3 a made of an insulator or anonmagnetic metal (aluminum, copper or the like), and windings 3 b.

[0054] The ring-like permanent magnet 12 is secured on the ring-likesteel plate 2 c. It is noted that reference numeral 15 denotes a pipemade of a non-magnetic material such as SUS, and is fixed to the steelpipe 2 a, the permanent magnet 12 being interposed therebetween. Sinceno large force is exerted to the pipe 15, it may be fixed by means ofscrews. The reason why the pipe 15 is made of a nonmagnetic material issuch that the magnetic field of the permanent magnet 12 should beprevented from short-circuited by the pipe 15. Further, a lid 17 made ofa nonmagnetic material is attached to one end part of the pipe 15, and arod 8 secured to the movable core 1 extend thererthrough. Thus, axialdeviation of the movable iron core 1 is prevented by the lid 17, theconvex steel member 2 b, the coupling member 7 and the rod 8.

[0055] The distance X between the end face of the plunger 5 and theconvex steel pipe 2 b is shorter than the distance L between thedisc-like steel plate 6 and the permanent magnet 12 in order to preventthe disc-like steel plate 6 from impinging upon the permanent magnet 12so as to damage the latter.

[0056] Explanation will be made of the operation of the electromagnet 10in this embodiment with reference to FIGS. 6 to 9 which are sectionalviews illustrating the electromagnet 10, reference numerals forexplaining the structure thereof being indicated in the right side partof the figure while a configuration of magnetic fields is shown in theleft side part thereof.

[0057]FIG. 6 shows a condition just after a start of attraction. Bothdistance X between the end face of the plunger 5 and the convex steelmember 2 b and distance L between the disc-like steel plate 6 and thepermanent magnet 12 are longer than a distance g between the permanentmagnet 12 and the plunger 5, and the magnetic field Bm created by thepermanent magnet 12 only affects upon a part around the permanent magnet12 as shown in FIG. 6. Thus, a drive force exerted to the movable ironcore 1 is extremely small. When the coil 3 is energized by an externalpower source (which is not shown), the magnetic field Bc created by thecoil current exerts an attracting force FO to the end face of theplunger 5, and accordingly, the movable iron core 1 starts its downwardmovement. Since the distance g between the side surface of the plunger 5and the ring-like steel plate 2 c is set to be longer than the length ofstroke of the movable iron core 1, the magnetic flux Φc created by thecoil current passes through a magnetic path 04. It is required topreviously set the direction of the coil current and the direction ofthe polarity of the permanent magnet 12 so as to extend the magneticfield Bc created by the coil current and the magnetic field Bm of thepermanent magnet Bm in a direction indicated by the arrow shown in FIG.6. It is noted that the direction of the magnetic field Bc and thedirection of the magnetic field Bm may be reversed from each other atthe same time.

[0058] When the movable iron core 1 is driven by the attracting forceFO, a condition shown in FIG. 7 is immediately effected. Along with themovement of the movable iron core 1, the gap L between the disc-likesteel plate 6 and the permanent magnet 12 is decreased so as to beshorter than the gap g between the plunger 5 and the ring-like steelplate 2 c (g>L), and accordingly, the magnetic field Bm of the permanentmagnet 12 passes through a magnetic path 05. That is, as the movableiron core 1 advances, the attracting force FO is exerted to the end faceof the plunger 5, and an attracting force F1 is also effected betweenthe disc-like steel plate 6 and the permanent magnet 12. Further, theelectromagnet Bm of the permanent magnet 12 passes through opposedsurfaces of the plunger 5 and the convex steel member 2 b, andaccordingly, the attracting force FO becomes further larger.

[0059] After completion of the iron core 1, when the coil 3 isdeenergized, the attracting force FO and the attracting force F1 areeffected by the magnetic flux Φm of the permanent magnet 12, and thiscondition is maintained.

[0060] Meanwhile, the release operation is carried out by energizing thecoil 3 with a current in a direction reverse to that during attraction,as shown in FIG. 8. The magnetic field Bc created by the coil currentruns through a magnetic path 06 so as to cancel out the magnetic fieldBm created by the permanent magnet 12, the attraction force FO isdecreased, and accordingly, the movable iron core 1 is moved upward bythe load force.

[0061] Explanation will be made of technical effects and advantagesobtained in this embodiment. Similar to the electromagnet in theembodiment 1, the magnetic field created by the coil current does notdirectly affect upon the permanent magnet 12, and accordingly, noreverse energy is exerted even during release operation. Thus, a risk ofdemagnetization of the permanent magnet 12 can be avoided, andtherefore, the electromagnet can have a long use life and a high degreeof reliability. Further, the permeability of the permanent magnet 12 issubstantially equal to that of the air, and accordingly, should thepermanent magnet 12 be present in the magnetic path created by the coilcurrent, the magnetic resistance as viewed from the coil would becomehigher. Upon a start of operation, a gap which is the sum of the strokeand the thickness of the permanent magnet 12 is present, resulting in anincrease in required ampere turn. In the electromagnet 10 in thisembodiment, no permanent magnet is present in the magnetic path createdby the coil current, the magnetic resistance becomes lower, andaccordingly, the efficiency becomes higher.

[0062] Further, the electromagnet in this embodiment can offer thefollowing technical effects and advantages. In the electromagnet in thefirst embodiment causes such a problem that attraction is again effectedduring release operation if excessive current is applied to the coil 3since the attracting force F1 is effected between the disc-like steelplate 6 and the magnetic protrusion 4 by the magnetic field Bc createdby the coil current. Thus, it is required to provide a measure forlimiting the coil current through the balance with the load force, andcutting off the coil current just after completion of release operation.However, there is no part where an attracting force is produced by themagnetic field Bc by the coil current in the electromagnet in thisembodiment, and accordingly, it is not required to provide a measure forlimiting the coil current through the balance with the load force, andcutting off the coil current just after the completion of releaseoperation.

[0063] (Embodiment 3)

[0064] Explanation will be hereinbelow made of a third embodiment of thepresent invention with reference to FIGS. 9 (in a turn-on condition) and10 (in a turn-off condition). FIGS. 9 and 10 are sectional viewsillustrating an electromagnet 10 in this embodiment, when a switchingdevice which is coupled to the electromagnet is turned on (FIG. 9) andwhen the switching device which is coupled to the electromagnet isturned off (FIG. 10), respectively. The turn-on condition and theturn-off condition, which will be taken in the following description,are conditions of the electromagnet obtained when the switching devicewhich is coupled to the electromagnet is turned on and off,respectively.

[0065] The coil 3 is composed of a bobbin 3 a made of an insulator ornonmagnetic metal (aluminum, copper or the like), and windings 3 b.

[0066] The electromagnet 10 as shown is composed of the coil 3, amovable iron core adapted to be moved on the center axis of the coil 3and made of a magnetic material, a stationary iron core configured tocover axially opposite end surfaces and the outer peripheral surface ofthe coil 3 and made of a magnetic material, a power source which is notshown, for applying a forward current and a reverse current to the coil.When the coil is applied thereto with a forward current, the movableiron core is moved in a direction toward the stationary iron core, thatis, in a direction from the right to the left as viewed in the figure.It is noted that the right and the left sides of FIG. 9 correspondrespectively to the upper and lower sides in view of the direction ofthe movement of the movable iron core.

[0067] The stationary iron core is composed of a square planar plate 2 dwhich is a stationary iron core upper member configured to cover one ofthe opposite end surface of the coil 3, and which is formed in itscenter part with a circular opening concentric with the coil 3, a squareplanar plate 2 f which is a stationary iron core lower member configuredto cover the other of the opposite end surfaces of the coil, and whichis formed in its center part with a circular opening concentric with thecoil 3, and a steel pipe 2 e which is held between the two square planarplates 2 d, 2 f and which covers the outer peripheral surface of thecoil 3, a cylinder 2 g which arranged on the upper surface of the squareplanar plate 2 f, concentric with the steel pipe 2 e. The square planarplate 2 d, the square planar plate 2 f, the steel pipe 2 e, and thecylinder 2 g are all made of magnetic materials. The square planar plate2 f and the cylinder 2 g are fixed together by screws, but may be weldedtogether. Further, they may, of course, be integrally formed by cuttingone and the same material.

[0068] A disc-like permanent magnet 12 formed at its center with acircular opening is arranged on the square planar plate 2 d, beingattracted thereto, and is secured thereto with an adhesive. Thepermanent magnet 12 may be made of any one of a material of a neodymiumgroup, a samarium group, an alnico group, a neodymium bond group and aferrite group. Further, although the permanent magnet 12 as shown is asingle ring magnet, it should not be in an integral ring-like shape, butplanar magnets having different shapes such a rectangular shape, acircular shape or the like may be distributed on the square planar plate2 d. However, even in this case, it is required to set the areas of thesurfaces of the magnets opposed to a cylindrical planar plate 6 a whichwill be detailed later so as to effect a required attracting force.

[0069] The movable iron core is composed of a nonmagnetic rod 19piercing through the opening of the square planar plate 2 d, the openingof the square planar plate 2 f, the steel pipe 2 e and the cylinder 2 gat their centers, a magnetic cylindrical plunger 15 fitted on and fixedto the rod 19, and the magnetic cylindrical planar plate 6 a which isarranged on the upper side of the plunger 5 through the intermediary ofa thin plate 21 which is a magnetic member and which is fixed to the rod19. The lower surface of the cylindrical planar plate 6 a is opposed tothe upper surface of the square planar plate 2 d with the permanentmagnet 12 intervening therebetween, and the outer peripheral surface ofthe plunger 5 is opposed to the inner peripheral surface of the coil 3.That is, the outer diameter of the plunger 5 is smaller than any of theinner diameter of the coil 3, the diameter of the center opening of thepermanent magnet 12 and the diameter of the center opening of the squareplanar plate 2 d, and accordingly, it can axially movable therethrough.However, the outer diameter of the cylindrical planar plate 6 a islarger than the diameter of the center opening of the permanent magnet12, and accordingly, it can not pass through the center opening of thepermanent magnet 12. Further, the plunger 5 and the cylindrical planarplate 6 a are secured to the rod 19, threadedly or by means of aretainer.

[0070] Further, the center opening of the permanent magnet 12 and thecenter opening of the square planar plate 2 d are concentric with eachother and have an equal diameter. Further, the thickness t of thepermanent magnet 12 is set to be larger than the gap g1 between theinner peripheral surface of the center opening of the square planarplate 2 d and the outer peripheral surface of the plunger 5.

[0071] The outer diameter of cylinder 2 g is smaller than the innerdiameter of the coil 3, and is set to be equal to the outer diameter ofthe plunger 5. Further, the inner diameter of the cylinder 2 g is set soas to allow the rod 19 to freely pass therethrough. That is, the lowersurface of the plunger 5 is opposed to the upper surface of the cylinder2 g, and accordingly, when the movable iron core is axially movedleftward, the movable limit thereof is determined by a point where thelower surface of the plunger 5 comes into contact with the upper surfaceof the cylinder 2 g.

[0072] A nonmagnetic pipe 15 a (which is made of stainless steel in thisembodiment) is arranged on the upper side of the permanent magnet 12,concentric with the coil 3, and is held between the permanent magnet 12and a square planer plate 18 which may be made of magnetic ornonmagnetic materials. Holes are formed in the four corners or twodiagonal corners of the square planar plate 2 f, the square planar plate2 d and the square planar plate 18. The holes can receive therethroughrods 14 having their opposite end parts formed with threads. Byfastening the opposite end parts of the rods 14 with nuts, there are allfixed together.

[0073] The square planar plate 18 and the square planar plate 2 f areformed therein with bores which are concentric with the coil, andthrough which the rod 19 can pass, and these bores are fitted thereinwith bearings such as dry bearings so as to reduce the friction withrespect to the rod 19 sliding therethrough, thereby it is possible tosave maintenance works.

[0074] Referring to FIG. 9 which shows the turn-on condition of theelectromagnet, the holding condition is effected by the attraction force(produced by a magnetic flux Φ1). That is, in the turn-on condition, thegap g3 between the lower surface of the plunger 5 and the upper surfaceof the cylinder 2 g is held to be zero, that is, the lower surface ofthe plunger 5 and the upper surface of the cylinder 2 g are held so asto be made into contact with each other. Instead of direct contactbetween the lower surface of the plunger 5 and the upper surface of thecylinder 2 g, a thin nonmagnetic material may be held therebetween.

[0075] During assembly of the electromagnet, the number of thin plates21 to be held between the plunger 5 and the cylindrical planar plate 6a, which have been previously prepared and which have an equalthickness, is changed in order to adjust the size of the gap g2 betweenthe permanent magnet 12 and the cylindrical planar plate 6 a to adesired value. The reason why the gap g2 is required, is such that, whenthe cylindrical planar plate 6 a bumps directly upon the permanentmagnet 12 during turn-on operation, the permanent magnet 12 isdemagnetized, causing the use life of the permanent magnet 12 to beshortened.

[0076] Further, by changing the number of thin plates 21, the gap g2 isdecreased to a small value which is possibly zero so as to decrease themagnetic resistance in order to increase the attraction force. As aresult, even though the permanent magnet 12 is thinned, or even thoughthe bulk of the permanent magnet 12 is reduced by decreasing its outersurface for attracting the square planar plate 2 d, a conventionalattracting force can be ensured. Thus, the cost of the permanent magnet12, which greatly depends upon the bulk of the permanent magnet, can bereduced, thereby it is possible to provide a small-sized and inexpensiveelectromagnet. Further, by changing the number of thin plates 21, thegap 2 g in a turn-on condition can be set to a nearly desired constantvalue, the attraction force and the turn-on and -off characteristics ofthe permanent magnet can be stabilized, thereby it is possible toenhance the reliability of the permanent magnet.

[0077] It is noted that, instead of changing the number of thin plateshaving an equal thickness so as to adjust the value of the gap, plateshaving slightly different thickness, which have been previously preparedare used by selecting an appropriate thickness, singularly or incombination in order to adjust the above-mentioned gap.

[0078] Next explanation will be made of turn-on and -off operation withreference to FIG. 11 (turn-on operation) and FIG. 12 (turn-offcondition).

[0079] During the turn-on operation shown in FIG. 11, a current (forwardcurrent) is applied from the power source which is not shown to the coil3 so that the coil produces a magnetic field in the same direction asthat effected by the permanent magnet 12. That is, the coil current andthe permanent magnet 12 produce magnetic fluxes Φ1, Φ2 as shown in FIG.11 so as to produce an attracting force for moving the cylindricalplanar plate 6 a leftward in the figure, that is, a force for attractingthe movable iron core to the stationary core. This attraction force isproduced both gaps between the plunger 5 and the cylinder 2 g andbetween the cylindrical plate 6 a and the permanent magnet 12. That is,the force F1 is effected between the cylindrical plate 6 a and thepermanent magnet 12, and the force F2 is effected between the plunger 12and the cylinder 2 g. The force F2 during turn-on operation is producedby a magnetic flux obtained by synthesizing the magnetic flux Φ2 and Φ1.

[0080] During the turn-off operation shown in FIG. 12, a current reverseto the current during turn-on operation, is applied to the coil 3 fromthe power source which is not shown. During the turn-on operation, thesum of the force F1 produced in the gap between the cylindrical plate 6a and the permanent magnet 12 by the magnetic flux Φ1 and the force F2produced in the gap between the plunger 5 and the cylinder 2 g by themagnetic flux Φ1 is greater than a force FO which is applied to the rod19 in the rightward direction in the figure, by a cut-off spring whichis not shown. That is, the force of the permanent magnet 12 overcomesthe force of the cut-off spring, and accordingly, the turn-on conditionis held. In this condition, when the reverse current is applied to thecoil 3, a magnetic flux Φ5 is produced in a direction reverse to that ofthe magnetic flux Φ1, and accordingly, the magnetic flux Φ1 is weakenedby the magnetic flux Φ5. This weakened magnetic flux (or the magneticflux Φ1 and the magnetic flux Φ5 in the reverse direction) produces aforce. F2 b in the gap between the plunger 5 and the cylinder 2 g. SinceF2 a>F2 b, the force applied to the movable iron core leftward as viewedin the figure becomes small, that is, F0>(F1+F2), the turn-off operationis started.

[0081] At this time, since the thickness t of the permanent magnet 12 isset to be greater than the gap g1 between the inner peripheral surfaceof the center opening of the square planar plate 2 d and the outerperipheral surface of the plunger 5, the magnetic flux Φ5 produced bythe reverse current does not extend through the permanent magnet 12 asshown in FIG. 12. It is because the magnetic permeability of thepermanent magnet 12 is substantially equal to that of the air. Themagnetic flux Φ5 produced by the reverse current passes through amagnetic path having a low magnetic resistance, as shown in FIG. 12.Should the permanent magnet be applied with the reverse magnetic fluxcontinuously for a long time, the demagnetization would be caused.However, according to the present invention, since no reverse magneticflux is applied to the permanent magnet. The probability ofdemagnetization becomes less, thereby it is possible to provide anelectromagnet having a long use life and a high degree of reliability.

[0082] (Embodiment 4)

[0083] Explanation will be herein made of a fourth embodiment of thepresent invention with reference to FIGS. 13 and 14.

[0084] In this embodiment, an electromagnet 10 stated in the embodiment1 to the embodiment 3 is applied in an actuating mechanism for aswitching device. FIG. 9 is a lateral sectional view for a three-phaseswitching device 20 in which the electromagnet 10 stated in theembodiment 2 is applied. Although explanation will be made of the vacuumswitching device in this specification, the permanent magnet 10according to the present invention can be applied in other circuitsbreakers including a gas switching device. Further, while explanationwill be made of such an arrangement that the electromagnet 10 stated inthe embodiment 2 is applied, the electromagnet stated in the embodiment1 or the embodiment 2 may be also applied.

[0085] The vacuum switching device 20 is composed of vacuum bulbs 30, anactuating mechanism part 40, an insulator frame 31, a control circuit 51and a manipulation space 50 for accommodating the electromagnet 10. Thevacuum bulbs 30 are arranged for three phases in the depthwise directionof the surface of the figure. Three vacuum bulbs 30 are coupled to oneanother by a shaft 41 in the operating mechanism 40, and are actuated bythe single electromagnet 10.

[0086] A vacuum is held in each of the vacuum bulbs 30 by a vacuumcontainer composed of upper and lower end plates 32 and an insulatorcylinder 33. A stationary contact 37 and a movable contact 38 arearranged in the vacuum bulb 30, and are adapted to make contact witheach other or separate from each other so as to effect turn-on and offoperation. The stationary contact 37 is fixed to a stationary conductor35, and is electrically connected to a stationary side feeder 39.Meanwhile, the movable contact 38 is fixed to a movable conductor 36,and is connected to a movable side feeder 62 through the intermediary ofa flexible conductor 61. Bellows 34 are connected at opposite ends tothe movable conductor 36 and the end plate 32, respectively. Thestationary contact 37 and the movable contact 38 can be made intocontact with and be separated from each other while a vacuum conditionis maintained by the bellows 34.

[0087] The vacuum bulbs 30 and the electromagnet 10 are both coupled tothe shaft 41, and accordingly, a drive force produced by theelectromagnet 10 is exerted to the movable conductor 36. The movableconductor 36 is electrically insulated from the operating mechanism bythe insulator rod 36 by the insulator rod 63, and is coupled to a lever42 fixed to the shaft 41. The movable iron core 1 in the electromagnet10 is coupled to a lever 44 by means of the connecting member 9.

[0088] Through turn-on operation, a press contact spring 43 and aturn-off spring 45 should be urged simultaneously. The press contactspring applies a press-contact force to the contacts during turn-onoperation, and the turn-off spring 45 carries out turn-off operation.

[0089] The press contact spring 43 is incorporated in an insulator rod63. FIG. 10 shows a structure around the press contact spring 43. Themovable conductor 36 is fixed to a connecting member 43 b, and theconnecting member 43 b is coupled to a press contact spring holder 43 aby means of a pin 43 c. A hole having a diameter slightly larger thanthat of the pin 43 is formed in the connecting member 43 b, and anelliptic hole 43 d is formed in the press contact spring holder 43 a.During turn-on operation, when the stationary contact 3 and the movablecontact 38 are made into contact with each other, the pin 43 c startsits movement in the elliptic hole 43 d (downward direction in thefigure), so as to continuously compress the press contact spring 43until the turn-on operation is completed. Meanwhile, the turn-off spring45 is continuously held between a top plate 46 of the operatingmechanism 40 and a plate 47 fixed to the connecting member 9. Theturn-off spring 45 is always compressed during turn-on operation.

[0090] Explanation will be made of the operation of the switching device20. When the coil 3 is energized so as to produce the magnetic field Bcshown in FIG. 7, the movable iron core 1 is driven downward by theattracting force FO, and accordingly, the movable conductor 36 is movedupward so that the contacts are turned on. Even though the current tothe coil 3 is cut off after completion of the turn-on operation, thiscondition is maintained by the attracting force of the permanent magnet12. During turn-off operation, when the coil 3 is energized by a currentin a direction reverse to that during turn-on operation, the magneticfield Bm of the permanent magnet is cancelled out, as shown in FIG. 8,so that the attracting force FO is decreased, and accordingly, themovable conductor 36 is driven downward by the force of the turn-offspring 45.

[0091] Next, explanation will be made of technical effects andadvantages of this embodiment. By applying the electromagnet 10 in theembodiment 1 or 2 in the switching device, a long use life of about 20years and several times of operation, greater than 10,000 times, can beensured without demagnetizing the permanent magnet 12 used for holding aturn-on condition. That is, it is possible to provide a switching devicehaving a long use life with a high degree of reliability.

[0092] In the above-mentioned fourth embodiment, although explanationhas been made of such an arrangement that the switching device device isoperated by a single electromagnet, a switching device of a largecapacity, which requires a large opening and closing force usually usesa plurality of electromagnets so as to produce a force corresponding toa capacity of a load. In this case, the number of electromagnets havingreference dimensions, which have been prepared beforehand, is adjustedin order to produce a desired opening and closing force.

[0093]FIGS. 15 and 16 shows switching devices each using fourelectromagnets, each of which is a plan view illustrating a switchingdevice similar to the switching device shown in FIG. 13 while the topplate 46 of the operating mechanism 40, the insulator frame 31, thecontrol circuit 51, the stationary side feeder 39, the movable sidefeeder 62 and the like are removed, and which explain how theelectromagnets are mounted to the shaft 41.

[0094] In the arrangement shown in FIG. 15, vacuum valves 30 a, 30 b, 30c respectively corresponding to three phase paths are mounted on theshaft 41 by means of levers 42 a, 42 b, 42 c, respectively, andelectromagnets 10 a, 10 b, 10 c, 10 d having one and the same shape, andone and the same specification are coupled to shaft 41 by means oflevers 44 a, 44 b, 44 c, 44 d, respectively. That is, the fourelectromagnets apply drive forces to the shaft 41, independent from oneanother.

[0095] In the arrangement shown in FIG. 16, the vacuum valves 30 a, 30b, 30 c are coupled to the shaft 41 in the same way as that of thearrangement shown in FIG. 15, but the electromagnets are coupled to theshaft 41 in a way different from that of the arrangement shown in FIG.15. Referring to FIG. 16, the levers 44 a, 44 b are coupled to theopposite ends of the shaft 14, and a coupling rod 52 for coupling thelevers 44 a, 44 b with each other, is pivotally connected to theassociated ends of the levers 44 a, 44 b. The electromagnets 10 a, 10 b,10 c, 10 d having one and the same shape, and one and the samespecification are coupled to the coupling rod 52, and accordingly, thedrive forces of the permanent magnets 10 a, 10 b, 10 c, 10 d are appliedto the shaft 14 through the intermediary of the coupling rod 52 and thelevers 44 a, 44 b.

[0096] Since any of both arrangements uses the electromagnets 10 a, 10b, 10 c, 10 d having one and the same shape, and one and the samespecification, a switching device mechanism using a plurality ofpermanent magnets can be provided with a convenient configuration.

[0097] With the electromagnet according to the present invention, andwith the operating mechanism for a switching device device, using theelectromagnet, no reverse magnetic flux is applied to the permanentmagnet, and accordingly, it is possible to provide an inexpensiveproduct which is small-sized and which is highly reliable. Further, thegap between the permanent magnet and the movable iron core which movesto and from the permanent magnet can be adjusted, it is possible toprovide a product which is inexpensive and which is highly reliable.

1-10. (Cancelled)
 11. An electromagnet composed of a coil having anupper surface and a lower surface, and an inner peripheral surface, amovable iron core adapted to move on a center axis of the coil, astationary iron core provided so as to surround the upper and lowersurfaces and an outer peripheral surface of the coil, and a power sourcefor applying a current to the coil forwardly and reversely, the movableiron core being moved toward the stationary iron core when the coil isforwardly energized, wherein the stationary iron core includes astationary core upper member provided so as to cover one axial end ofthe coil, and having an inner peripheral surface and an upper surface, apermanent magnet is provided on the upper surface of the stationary coreupper member, and the movable iron core is composed of a planar platemember having a surface which is opposed to the upper surface of thestationary core upper member with the permanent magnet interveningtherebetween, and a plunger having a cylindrical surface opposed to theinner peripheral surface of the coil, the inner peripheral surface ofthe stationary iron core upper member and the cylindrical surface of theplunger defining therebetween a gap g1 which is smaller than a thicknessof the permanent magent in the axial direction of the coil.
 12. Anelectromagnet as set forth in claim 11, further comprising an currentcircuit for selectively applying a forward current and reverse currentto the coil, wherein when a forward current is applied, a magnetic fieldin the same direction as that of a magnetic field produced by thepermanent magnet is produced so as to effect attraction, but when areverse current is applied, the magnetic field produced by the permanentmagnet is cancelled out so as to effect release operation.
 13. Anelectromagnet as set forth in claim 11, wherein said permanent magnet isselected from a group consisting of a rare earth samarium-cobalt groupmagnet, a neodymium group magnet, an alnico group magnet and a ferritegroup magnet.